The UIO format is described in some detail in Sect 4.
Each entry has a type (e.g. ``label'', ``real'', ``character''),
an identifier (e.g. ``box'', ``time'', ``description''),
and additional information about array size (e.g. ``d=(-63:63,-63:63,-63:63)''),
data format (e.g. ``f=E13.6 p=4 b=4''),
and properties of the quantity (e.g. ``n=Density u=g/cm^3'').

Each start (``rhd.sta'') or final (``rhd.end'') model file has a structure
as shown above. The (``rhd.full'') file usually contains a sequence of these
data sets, which of course can also be used as start model of a simulation.

The axes xc1,
xc2,
and xc3 describe the positions of the cell centers.
The axes xb1,
xb2,
and xb3 contain the positions of the cell boundaries:
they have one element more than the corresponding cell centered quantity.

Cell boundaries should be centered in the middle between cell centers for
the best representation of radiative fluxes with MSrad3D.